The Virginia senator questioned the odds that Trump would have avoided saying anything about who would pay for the border wall while mocking the conflicting accounts over whether the wall came up during the sit-down.

The Republican presidential nominee has made the wall — and Mexico paying for it — a core element in his campaign. Trump said it didn't come up in his meeting Wednesday with Peña Nieto. But Pena Nieto tweeted that he had told Trump that Mexico wouldn't pay for the wall.

"I find that kind of ridiculous," Kaine said Thursday on NBC's "Today" show. "Even if it didn't come up, he choked and forgot to say that to the president of Mexico after he's been saying it every day for the last many months?"

Trump Booed Leaving New York Times

President Elect Donald Trump is booed as he walks through the lobby of The New York Times Building after a 75-minute meeting with Times journalists. The lobby of the Times building is open to the public, and a large crowd had gathered by the time he departed.

(Published Tuesday, Nov. 22, 2016)

Kaine told Matt Lauer and Savannah Guthrie that even if Trump's account is accurate, it showed he "folded under pressure" and "didn't have the backbone" to discuss the issue with the Mexican president.

"When he's looking the leader of Mexico in the eye, he can't bring himself to say it," Kaine said.

Lauer challenged Kaine's notion that the meeting was amateur diplomacy, noting that a "toned down" Trump appeared presidential alongside the Mexican leader.

"You know, I think the important thing about leadership is you got to be consistent. You can't say different things to different audiences," Kaine said. "And so, you know, he came back across the border and then it was all about Mexico is going to build a wall. Mexico is going to pay for it. He was divisive. He basically says America is going to be deportation nation. But when he's looking the leader of Mexico in the eye, he can't bring himself to say it."

Ask by Guthrie whether Trump prevailed in the war for optics by traveling to Mexico while Clinton spent the greater part of the last week fundraising in the Hamptons, Kaine challenged that assumption.

"I don't think so. Again, just do the contrast, the 24 hours of yesterday," Kaine said. "Donald Trump choked on the fundamental promise that he's making in this campaign when he had the opportunity to talk to the foreign leader about it by his words he didn't bring it up, by the leader's words, yeah, no did come up and I told Trump we're not paying for your wall. So that just shows that I think kind of not ready for prime-time but then back over on this side of the border, he just doubles down on this divisive deportation nation strategy."

Trump Takes Meetings at His New Jersey Golf Club

President-elect Trump interviewed more than a dozen candidates for his administration at his New Jersey golf club over the weekend, including Mitt Romney, Rudy Guliani, Chris Christie and Kansas secretary of state Kris Kobach, who has been tough on immigration, and others.

(Published Monday, Nov. 21, 2016)

Kaine also addressed recent polls that show a tightening race between the two White House hopefuls. Although Clinton maintains a lead over Trump, her favorability rates are decreasing.

"I've always assumed this race would be hard," he said. "We’re feeling good about our position in a number of the true battleground states, but we do not feel any sense of complacency."